Out of curiosity, what happens if you check to verify that the access.db file is actually successfully opening? Change that first line as follows:

dbmopen( %TEST, "/home/lab/access.db", 0666 ) 
    or die "Couldn't open database: $!\n";
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My first guess is that you're not successful in opening the database, and that extra "or die..." stuff will alert you to the problem.

Also, have a look at the documentation for dbmopen, where it says that the dbmopen function has been largely superseded by tie.